Patent Application
20140270731
Embodiments of the present invention generally relate to semiconductor processing systems and, more specifically, to solid state light sources for use in semiconductor processing systems.
Embodiments of the present invention generally relate to semiconductor processing systems and, more specifically, to solid state light sources for use in semiconductor processing systems.
Several applications that involve the thermal processing of substrates such as semiconductor wafers and other materials involve the process steps of rapidly heating and cooling a substrate. Examples of such processing include rapid thermal processing (RTP), physical vapor deposition (PVD) processing, and the like, which are used for a number of semiconductor fabrication processes.
During semiconductor fabrication processing, heat energy from lamps is radiated into the process chamber and onto a semiconductor substrate in the processing chamber. In this manner, the substrate is heated to a required processing temperature. Typically, the use of conventional lamps (tungsten-halogen, mercury vapor, arc discharge) or electrical heating elements has been the dominant approach to delivering energy to the substrate for dopant annealing, film deposition, or film modification. These processes are often thermally based and typically require high process temperatures ranging from 200 C to 1600 C, which can result in significant thermal budget issues that adversely affect device performance. In addition, the use of conventional lamps has associated high maintenance costs with respect to operating lifetime, material and energy usage. Conventional lamps emit radiation over a broad spectrum of wavelengths which can be detrimental to some instrumentation and/or result in an unintended response in the target substrate/film from the undesired wavelengths.
Arrays of solid state light sources, for example Light Emitting Diodes (LEDs), may be used instead of, or in addition to, conventional lamps for various semiconductor fabrication processes to address some of the foregoing issues. In order to achieve target irradiance levels on the order of 1e6 W/m̂2 that are comparable to the intensities required for RTP, high packing density of LEDs would need to be used.
However, heat dissipation and thermal management is important to the operation of ultra high intensity LED arrays. These LED arrays should remain at or near room temperature in order to extract the maximum brightness and long operating lifetime. There are many approaches to solving the heat dissipation issue, such as cold plates, heat pipes, or Peltier coolers. However, none of these solutions sufficiently addresses the heat dissipation requirements associated with LED arrays.
Specifically, cold plates are typically only good for 1 kW dissipation with 20 K rise in temperature. They can be designed for large area but for high power densities this is not enough. Heat pipes have thermal conductivities of 5,000 W/m/K to 200,000 W/m/K. They are effective in transporting heat from one point to another, but not in removing the heat from a system, where a heat sink is required. Finally, thermoelectric coolers (aka Peltier coolers) are capable of approx 1e5 W/m̂2 cooling but only available in small sizes. They are costly and require as much power input to operate as the electronics to be cooled.
Accordingly, the inventors have provided improved heat dissipation and thermal management devices for use with solid state light source array for use in semiconductor processing systems.
Apparatus for providing pulsed or continuous energy in a process chamber are provided herein. The apparatus may include a process chamber comprising a chamber body, a solid state light source array, having a plurality of solid state light sources disposed on a first substrate, to provide pulsed or continuous energy to the process chamber, and a cooling mechanism including a band pass filter to reduce an amount of reflected light from heating the solid state source array.
In some embodiments, an apparatus for providing pulsed or continuous energy in a process chamber may include a process chamber comprising a chamber body, a solid state light source array, having a plurality of solid state light sources, disposed on a first substrate, to provide pulsed or continuous energy to the process chamber, and a cooling mechanism including a transparent window disposed over the solid state light source array forming a cooling channel disposed between the plurality of solid state light sources and the window configured to flow the coolant over the plurality of solid state light sources.
In some embodiments, an apparatus for providing pulsed or continuous energy in a process chamber comprising a chamber body, a solid state light source array, having a plurality of solid state light sources, disposed on a first surface of a substrate, to provide pulsed or continuous energy to the process chamber, and a cooling mechanism coupled to a second surface of the substrate to remove heat from the solid state light source array, the cooling mechanism including a base plate, a top plate, and a plurality of fins disposed between the base plate and the top plate.
Other embodiments and variations of the present invention are disclosed in greater detail below.
Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Embodiments of an apparatus for providing pulsed or continuous energy in a process chamber are provided herein. In some embodiments, the inventive apparatus may advantageously provide improved cooling and thermal management of solid state light sources used in process chambers for heating of substrates and other components disposed in a process chamber.
In the following description, the term substrate is intended to broadly cover any object that is being processed in a thermal process chamber. The term substrate may include, for example, semiconductor wafers, flat panel displays, glass plates or disks, plastic workpieces, and the like. In the following description solid state light point sources include light emitting diodes (LEDs) and LASERs. In addition, although described below in terms of LEDs or arrays of LEDs, LASERs and arrays of LASERs, other solid state light point sources may be used interchangeably in embodiments described herein.
The process chamber 100 may, for example, be adapted for performing thermal processes and illustratively comprises a chamber body 110, support systems 130, and a controller 140 that includes of a CPU 142, memory 144, and support circuits 146. The process chamber 100 depicted in
The process chamber 100 includes a energy source 138, which may include a plurality of LEDs or array(s) of LEDs arranged in zones, wherein each zone of LEDs is separately controllable. In some embodiments, the energy source 138 may be a conventional lamp augmented with LEDs strewn about areas of the lamp head that had previously not been a light-emitting surface, increasing usage of the heat source surface area.
In
In some embodiments, a cooling mechanism 150 may be used to cool the energy sources 138. Some exemplary cooling mechanisms 150 may include, for example, the use of heat sinks, heat exchange fluid cooling channels or fins, band pass filters, etc. coupled to (as discussed below) the energy sources 138. In some embodiments, the substrate on which the light sources are mounted or grown on may itself be a heat sink used for cooling. In other embodiments, energy sources 138 may be cooled by a gas or liquid circulated around or proximate to the energy sources 138.
A substrate support 124 included in chamber 100 may include parts of a process kit 125 which may be adapted to work with various embodiments of substrate supports and/or process chambers. For example, the process kit 125 may include elements of the substrate support 124, such as edge ring 126 and an edge ring support 127.
During processing, the substrate 101 is disposed on the substrate support 124. The energy source 138 is a source of radiation (e.g., heat) and, in operation, generates a pre-determined temperature distribution across the substrate 101. In embodiments, where the heat source includes LEDs (as shown in
In the exemplary processing chamber 100 described above, energy source 138 may be used to illuminate and heat the surface of a substrate to process the near surface region of the substrate. LED light sources offer a variety of advantages including higher efficiency and more rapid response times. Pulse widths are selectable and can range to less than a millisecond to more than a second.
In some embodiments, the LED energy source 138 may be used in conjunction with processing chambers to form films, treat dopants, change process gases (e.g., break bonds), and reorder the substrate itself. Additional high temperature substrate processing may benefit from LED heating as even higher output intensities become available. LEDs offer advantages when used to process the near surface region of a substrate. LEDs last a long time and allow the output intensity to be chosen independent from the wavelength(s) of the output illumination. Light emitting diodes (LEDs) may consist of gallium nitride, aluminum nitride, combinations thereof or other III-V materials grown on a substrate constructed to emit light close to one or more wavelengths determined by the bandgap of III-V materials in the active region. A phosphor may also be used to convert an emitted wavelength to a longer wavelength, reducing the energy of an emitted wavelength. It will be understood that the solid state sources described herein and depicted in the remaining figures may employ a phosphor in order to enhance absorption or enhance a chemical reaction.
Depending on the chemistries involved, illuminating a surface in the presence of gas precursor can enhance the rate of chemical reactions by thermal or other means. For example, the light may excite gas phase molecules, adsorbed molecules, or even excite the substrate to promote a chemical reaction on the surface. The wavelength of the LED may be selected to promote desirable film processes by, for example, choosing a wavelength which is resonant with a molecular electronic transition in order to enhance a reaction rate. The wavelength may also be chosen to enhance absorption of the radiation by the substrate, thereby heating the substrate more efficiently.
In some embodiments, each energy source 138 in
In some embodiments, energy source 138 may illustratively be between 100 mm and 480 mm in length and between 100 mm and 480 mm in width. In addition, various size energy sources 138 may be used as required or desired in any particular application. In some embodiments, each LED array 204 may be about 20 mm by about 20 mm square, although other size LED arrays 204 may be used. Each LED array 204 may contain between about 50 and about 500 LEDs 206 (e.g., 384 LEDs as shown in
In addition, LEDs 206 and LED arrays 204 have faster on-off switching times than incandescent lamps. In some embodiments, the LEDs have on-off switching times on the order of nanoseconds versus hundreds for milliseconds for incandescent lamps. Specifically, in some embodiments, the LEDs have a switch-on time from about 0.5 nanoseconds to about 10 nanoseconds and a switch-off time from about 0.5 nanoseconds to about 10 nanoseconds. Faster on-off switching times enables shorter thermal exposures. The use of small form factor LEDs as described above makes it possible to design conformal high intensity illumination systems at a lower cost of ownership, longer operating lifetime (˜100 k hours) and in the case of UV LEDs, an environmentally sensitive alternative to toxic mercury vapor based lamps.
In some embodiments, the LED array 204 can be individual LED chips 206 with different wavelengths, or the LED array 204 can be a collection of LED lamps with different wavelengths. The LEDs can be multiplexed/rasterized such that certain LEDs with certain wavelengths are activated at one time. For example, at time 1t, only λ1 LEDs are active, at time 2t only λ2 LEDs are active, etc. Thus, the LEDs in LED array 204 can be grouped and separately controlled by a controller (e.g., controller 140).
In some embodiments, the reflectors 208, 210 are configured to reflect the light and heat energy emitted from the LED towards the desired target (e.g., wafer substrate, or other process chamber component, etc.). In the case of LASERS, the reflectors 208, 210 could direct the light off of the LASER beams' axis to heat a wafer substrate or desired process chamber component. The reflectors 208 and 210 may be angled to reflect radiated LED light in a desired direction. In some embodiments, the angles of the incline of the reflector surfaces from the LED substrate 202 surface is between about 45 to 55 degrees from an axis of the LED extending in a direction toward where light energy is desired (e.g., for a planar array of LEDs, the axis may be perpendicular to the planar array), however, any angle which maximizes the angle and desired length of the reflector based on the space available between two neighboring LEDs 206, or LED arrays 204, may be used. In other embodiments, the surfaces of the reflectors 208, 210 may be perpendicular to the surface of the LED substrate 202. Still, in other embodiments, the surface of the LEDs 206 may be angled instead of, or in addition to, the surface of the reflector. In some embodiments, the height of the reflectors 208, 210 is at least the same height as the height of the LEDs 206, but may be higher or lower than the LEDs 206 as required.
In some embodiments each LED 206 may be individually mounted on LED substrate 202. Each LED 206 may be mounted to the substrate via eutectic bonding, including wire-bond-free direct attach LEDs. To direct attach LEDs to a substrate, a flux is first disposed on the substrate surface to which the LEDs will be attached. The LEDs are then disposed over this surface. The LEDs and the surface are then heated with a certain heating profile. An amount of solder disposed on the bottom of the LED will melt with help of the flux, and will attach the LED to the fluxed surface. In some embodiments, each LED 206 may be grown on LED substrate 202. The LEDs 206 may be individually grown, grown in groups/sections, or grown all together at the same time. In some embodiments, the LED substrate 202 that LEDs 206 are grown on may be an n-type substrate, with an electrode (e.g., 214) attached to the p-type layer 240 deposited on its surface. Silicon substrates or sapphire substrates may be used as well. The substrate can be any material that is thin enough, or has a high thermal conductivity, such that it is able to dissipate heat from the LEDs quickly while also providing electrical isolation of the LEDs from the rest of the system. This can be done by using an electrically isolating material. LEDs can be grown on any material where the lattice structure of the substrate can be made to match the lattice structure of the LED material through, but not limited to, direct deposition, application of a buffer layer, and/or any type of stress relaxation. In some exemplary embodiments, the substrate can be ceramic. In some embodiments, islands of non-substrate material/chemistries may be grown or included in the substrate to help facilitate LED growth.
In some embodiments, the LEDs 206 in LED arrays 204 are connected in series. In some embodiments, the LEDs 206 are disposed on LED substrate 202 in a recursive pattern on a first surface of the substrate 202. The recursive pattern maximizes the use of the available surface area of the first surface of the substrate 202. In some embodiments, the recursive pattern is a serpentine structure including a plurality of rows of LEDs 206, such that each row of LEDs 206 is electrically coupled to at least one other row of LEDs 206 as shown in
Due to the high packing density of the LED arrays 204 described in embodiments of the present invention, some embodiments may require the use of a cooling mechanism 150 for heat dissipation and thermal management as described below with respect to
In some embodiments, the band pass filter 402 may reduce the heat built up of the LED array 204 by reducing/filtering the amount of radiation reflected and re-emitted back to the LED array 204. Specifically, a band pass filter 402 advantageously allows for a narrow range of wavelengths pass for a specific process as desired. For example, in some embodiments, a specific range of LED wavelengths may be required for purposes of film modification, film cure specific wavelength, and the like. The band pass filter 402 will filter out all other wavelengths emitted from the LEDs 206 and pass only the wavelengths desired for the process. For example, with respect to
When filtering/reflecting various wavelengths of light, the band pass filter 402 may get hot. In addition, additional cooling of the LEDs may be required. Thus, in some embodiments, the use of low temperature liquid immersion cooling may be used as shown and discussed with respect to
In some embodiments, the low temperature fluid could be ethylene glycol, alcohol, water, de-ionized water, oil or any combination thereof. In some embodiments, the low temperature circulating fluid 502 is a high resistivity coolant that doesn't react with the LEDs. In some embodiments, the liquid temperature can be less than 0 C, e.g. −40 C, depending on the coolant used.
The use of low temperature circulating fluid 502 advantageously reduces the overall thermal load on the LEDs 206, improving the LED array 204 performance and system lifetime. In the case of temperature sensitive LED light sources, liquid cooling may mitigate or solve issues related to keeping LEDs cool enough for over driving to extract more intensity.
In some embodiments, the cooling mechanism 150 may be a finned heat sink structure 602 with a coolant 610 flowed therethrough, as shown in
Referring back to
A coolant 610 may be delivered (e.g., from a coolant reservoir by a pump) at up to 60 gallons per minute through the finned heat sink structure 602. Depending on the fin structure and heat removal required, the flow rate may be reasonably high in order to ensure turbulent conditions at the heat sink/liquid interface which will reduce the boundary layer of the fluids and overall thermal resistance. For lesser heat removal requirements, the flow rate may be lower to provide a more laminar flow, reduce the pressure drop and required fluid inlet pressure. The coolant 610 could be any liquid. In some embodiments, water is used due to its high heat capacity, compatibility with most materials, and low cost. In some embodiments, other liquids such as antifreeze (e.g. any combination of water, ethylene glycol, diethylene glycol, propylene glycol, etc.), dielectric fluids (e.g. oil, silicone oil, mineral oil, fluorocarbon oil), or liquid gases (O2, N2, H2, CO2 etc) may be used. Embodiments of the finned heat sink structure 602 described herein advantageously improve cooling efficiency and can help manage the cyclical fatigue and cracking associated with system elements thermally expanding.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.
This application claims benefit of U.S. provisional patent application Ser. No. 61/777,521, filed Mar. 12, 2013, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61777521 | Mar 2013 | US |
